donkey's years

noun

, Informal.

1. a very long time; eons.

donkey's years

noun

1. informal.
   a long time

Word History and Origins

Origin of donkey's years¹

First recorded in 1895–1900; probably originally donkey('s) ears, as rhyming slang for years, with years replacing ears once the rhyming origin was forgotten

Idioms and Phrases

A long time, as in I haven't seen her in donkey's years . This expression punningly alludes to the considerable length of the animal's ears. [Early 1900s]